WASHINGTON (Reuters) – The national energy adviser for Mitt Romney’s presidential campaign, Oklahoma oil billionaire Harold Hamm, made political contributions that exceed federal legal limits by as much as 41 percent, according to data compiled by Reuters.

The data, based on public filings, showed that Hamm’s political donations exceeded the legal limits for individual donations to political parties, campaigns and political action committees (PACs) over the 2011-2012 election period.

Hamm, the CEO of oil and gas company Continental Resources, has given $164,700 to parties, PACs and candidates, including Romney, in the current two-year election cycle, in addition to an almost $1 million donation in April to the main Super PAC supporting Romney.

The $985,000 Hamm gave to Super PAC Restore Our Future is legal, because there is no limit on such giving. But his other federal contributions put him well over the legal limit of $117,000 in an election period for an individual donor. Hamm has also exceeded lesser limits both for individual contributions to candidates and to regular political action committees and parties by more than $20,000 each.

Reuters reporters alerted Hamm on Tuesday to the breach of limits and presented him data on Wednesday. The Wall Street Journal reported the donation violations earlier Thursday on its website.

Hamm’s political adviser, Mike Cantrell, said in an email on Thursday afternoon that Hamm had intended to break up the donations between himself and his wife, Sue Ann Hamm, which he said would have ensured that Hamm remained under legal contribution limits. The donations were made from a joint account, Cantrell said, but Hamm failed to make clear that they were donations split between Hamm and his wife.

“Apparently some committees and/or campaigns to which Harold and Sue Ann Hamm made contributions reported those as having been contributed solely by Harold Hamm. That was a mistake. Others appear to have been misallocated,” Cantrell told Reuters.

Cantrell said Hamm had believed that the contributions would be attributed 50 percent to Harold Hamm and 50 percent to Sue Ann Hamm, because under Oklahoma state campaign finance law, the maximum contribution limits are calculated on a per-family basis. Under federal law, contributions made from a joint bank account are split only if both parties sign the check.

Hamm “believed he was in compliance with all federal and state election laws. After notification from Reuters, Mr. Hamm had his contributions reviewed again,” Cantrell said. “Since this was brought to our attention, the recipient committees are being notified and requested to take appropriate steps to correct any errors.”

In an interview last week, conducted before the finance violation was clear, Hamm told Reuters he saw no conflicts of interest arising from his financial support and fundraising for Romney or other candidates.

Hamm helped Romney to devise his national energy policy platform for a white paper the campaign released last month. It focuses heavily on opening up more U.S. territory for oil drilling, which could benefit Hamm’s company, a top lease-holder in the prolific Bakken oil field of North Dakota.

“Everybody in America supports the candidates that are aligned with their beliefs and their philosophy. This goes back to First Amendment rights,” Hamm told Reuters. “We can support the candidate of our choice.”

Hamm might face penalties for the donation breaches, up to the excess amount he has contributed.

“The (Federal Election Commission) itself cannot impose a fine,” said Paul S. Ryan, senior counsel for the Campaign Legal Center, a Washington D.C. campaign finance organization. He noted that while the Department of Justice retains the authority to prosecute deliberate contribution violations, he hasn’t seen them pursue such cases.

The FEC said it couldn’t comment on any matters involving donations by individuals.

Aside from his Super PAC contribution earlier this year, Hamm and his wife, Sue Ann, have in total given $430,150 to candidates, PACs and political parties since 1999, with more than half of their overall total coming during this election cycle, according to data compiled from public filings.

Overall, the Hamms gave $367,050 to Republicans, more than six times as much as they gave to Democrats, including contributions to the presidential campaigns of Rudy Giuliani, John McCain and George W. Bush. During this election, less than four percent of the $235,550 they gave went to Democrats.